Chris Medland
F1 journalist in Barcelona

It's the end of a first week in new colours for Daniel Ricciardo, who has handed the Renault over to Nico Hulkenberg for the afternoon session (although like George Russell at Williams, Hulkenberg has yet to hit the track).

Ricciardo has been encouraged by the performance of the Renault, saying it responds to changes and feels like it has potential, but he says it's too hard to work out where that could leave the team due to a number of cars looking solid this week.

Reflecting on his new surroundings, though, Ricciardo says the relationship with both the team and Hulkenberg is off to a good start. "I feel like I am comfortable with everyone," Ricciardo said. "It does feel normal, walking into the meeting rooms and that, the debriefs, it feels familiar.

"The way everyone is engaging with me has been positive and they are certainly trying to draw as much as they can out of me, and to also see if Nico and me are on same page.

"Yesterday the main things we talked about were identical on where to improve the car, so that is a positive that we are both asking for the same things. It feels cozy."

1. Albon (Toro Rosso) 1:17.637 (59 laps) C5 tyre
2. Ricciardo (Renualt) 1:17.785 (34) C4
3. Bottas (Mercedes) 1:17.955 (23)
4. Hamilton (Mercedes) 1:17.977 (58) C4
5. Leclerc (Ferrari) 1:18.046 (113)
6. Giovinazzi (Alfa Romeo) 1:18.511 (105) C2
7. Grosjean (Haas) 1:18.563 (64) C4
8. Magnussen (Haas) 1:18.720 (33)
9. Gasly (Red Bull) 1:18.780 (103) C3
10. Norris (McLaren) 1:19.543 (88)
11. Stroll (Racing Point) 1:19.664 (59)
12. Hulkenberg (Renault) 1:20.095 (8)
13. Kubica (Williams) 1:21.706 (48)
14. Russell (Williams) Out lap (1)

Robert Kubica's first morning of testing yielded 48 laps and the slowest time, which is no surprise given the delays for Williams this week. Once he got out of the car he explained a bit about his day and said he only got 12 laps to try and get a feel for the car - carrying out aero tests and data gathering the rest of the time - so that's what he'll have to end the first week with.

There was huge interest in Kubica from both the media and fans, and while he spoke well there was also an undertone of frustration. The Pole says he is no more prepared for Australia than he was three months ago due to the lack of running, and although he praised the team for the quick car build once it was ready, there was also a bit of a dig at the delay.

Kubica says there is no point in Williams looking at lap times yet, but added: "I have to say when I saw the first couple of runs of other people on day one, I was impressed.”

(He was in there somewhere, honest.)

1. Albon (Toro Rosso) 1:17.637 (59 laps) C5 tyre
2. Ricciardo (Renualt) 1:17.785 (34) C4
3. Hamilton (Mercedes) 1:17.977 (58) C4
4. Leclerc (Ferrari) 1:18.046 (92) C3
5. Bottas (Mercedes) 1:18.356 (11)
6. Giovinazzi (Alfa Romeo) 1:18.511 (79) C2
7. Grosjean (Haas) 1:18.563 (64) C4
8. Gasly (Red Bull) 1:19.202 (78) C3
9. Magnussen (Haas) 1:19.389 (15)
10. Norris (McLaren) 1:19.543 (55)
11. Stroll (Racing Point) 1:20.026 (47)
12. Kubica (Williams) 1:21.706 (48)

Andrew Benson
BBC Sport’s chief F1 writer

Is he worried?

“Worried? It would be better to have a bit more ideas and a bit more feeling in the car, both from driver and car point of view but the reality is this so we have to keep working and hopefully the delays are only for testing. Australia is not far off. Everybody is concentrating on Barcelona and our car was late. Hopefully everything will be sorted for Australia.”

Is the car a step forward?

“In some ways it is a step forward, in others not. The question is, have we made a bigger step forward than back because of the regulations? In order to improve, we have to make a bigger step than the others or we will be where we were last year. It is not correct to talk about performance of the car or feelings. We see next week.

“It was not smooth morning but as usual of what you could expect of the first day in a new car. It is too early to talk about feelings. We will see next week."

Image source, Reuters

Andrew Benson
BBC Sport’s chief F1 writer

Robert Kubica's return to Formula 1 after an eight-year absence caused by the injuries suffered in his horrific rally crash back in 2011 is one of the stories of the season, and on Thursday he finally got his hands on the car he will race, after the delay in the introduction of the Williams car.

He said: “A mixed day between checking systems and trying to get a bit of data. It doesn’t feel like day four but felt like day one. I got 12 laps to get a feel for the car but at least most of the stuff we achieved. Not all. It was not an easy morning.”

Image source, Getty Images

George Russell is hanging around outside of the Williams garage, when Sky Sports have a word with him. He says: "The guys are changing the car from Robert's set up to my set up and we'll be out in 25-30 minutes.

"We are just putting miles on the car. Overall this day-and-a-half is setting us up for next week so we're going to try hard to get us in a better position for next week.

"The more laps we can get in now the better it is for everyone... so far so good."

Image source, PA

We have a few driver changes:

Lewis Hamilton is done for the week, after completing 58 laps today, so Valtteri Bottas is out next in the Mercedes.

Nico Hulkenberg will be out in the Renault and Kevin Magnussen will be out in the Haas.

That concludes this morning's session.

Alex Albon remains the quickest in the Toro Rosso, followed by Daniel Ricciardo and Lewis Hamilton.

We'll be back at 13:00 GMT for this afternoon's session.

Andrew Benson
BBC Sport’s chief F1 writer

The impression after three days of this test was that Ferrari were the team to beat, and it seems Mercedes feel the same way. Valtteri Bottas has not long ago finished a news conference, and he said: “They do seem very strong. No matter which kind of fuel load or engine modes they’re running, whatever you try to correct that for in any case they are quick. Both short runs and long runs. So I think we feel at this point they’re going to be a bit ahead.

“Obviously it’s impossible to make detailed calculations. It is very early days. With the new rules it’s going to be a big development race. We don’t think anyone is going with this type of car in this test to the first race, including us. We do have new parts coming for the first race. [But] we can’t really rely on that being an upgrade. We do need to, even with this spec of car, to try and make it better and quicker.”

Image source, Reuters

Kayleigh: Really really hope for good things from Lando this year, and he doesn’t end up on the McLaren scrap heap like the other mega babes- JB, Stoff... Williams aren’t looking too special at the moment so could be a tough year for Russell.

deaglan mcardle: have to say I'm generally impressed with the sheer reliability of the cars this week. None of the usual breaking down and out for several hours. Just some minor niggles on the face of it. Well except Williams issues of course.

CJEd: Good see Lance Stroll achieving his potential and taking Racing Point to the back of the grid.

Alex Albon is quickest, on the softest tyres (C5). But Charles Leclerc goes off into the gravel at Turn 5, but manages to continue on.

1. Albon (Toro Rosso) 1:17.637 (40 laps) C5 tyre
2. Ricciardo (Renualt) 1:17.785 (34) C4
3. Hamilton (Mercedes) 1:17.977 (42) C4
4. Leclerc (Ferrari) 1:18.046 (67)
5. Giovinazzi (Alfa Romeo) 1:18.511 (46) C3
6. Grosjean (Haas) 1:18.563 (64) C4
7. Gasly (Red Bull) 1:19.495 (51) C3
8. Norris (McLaren) 1:19.702 (39)
9. Stroll (Racing Point) 1:20.026 (41) C3
10. Kubica (Williams) 1:21.706 (40) C3

Andrew Benson
BBC Sport’s chief F1 writer

OK, tyres. In an attempt to simplify things this year, tyre supplier Pirelli has reduced the number of dry-weather compounds available through the year to five from seven, and at each race they will simply be called soft, medium and hard, indicated by red, yellow and white markings on the sidewall.

So far, so easy. But of course it’s not that simple. The soft, medium and hard at each race will not necessarily be the same as at another race - they will be chosen from the five options, which are known as C1 (for the hardest), C2, C3, C4 and C5 (for the softest) - once Pirelli have decided which compound set will be more suitable for each track's characteristics. So hard tyres for demanding tracks like Silverstone and Suzuka, for example, soft ones for undemanding ones (for tyres) like Monaco, Canada and so on.

The idea is that casual fans can be less confused by the names, but enthusiasts can still understand which tyre is being used at each track.

For testing, all five compounds are available. The three colours remain the same, but the C1 and C5 compounds will have white and red lettering, like the C2 and C4, and will be differentiated by the lack of what Pirelli call brackets on the sidewall - what others might call lines - between the logos. Not the easiest thing to spot at 200mph, but there you go.

The 2019 compounds are similar to last year’s hard (C1), medium (C2), soft (C3), ultra-soft (C4) and hyper-soft (C5), but just feature slight changes to compounds and construction.

Image source, Pirelli Twitter